1. Field of the Invention
The present invention relates to a three-dimensional radar apparatus which is carried, for example, on a ship and which preferably detects a target. The present invention also relates to a method for displaying a three-dimensional radar image. Especially, the present invention relates to a three-dimensional radar apparatus and a method for displaying a three-dimensional radar image in which image data, which is converted into two-dimensional rectangular coordinates (X, Y) as obtained by a conventional radar apparatus, is converted into image data (X, Y, Z) added with the height direction (Z axis) on the basis of its brightness value to perform three-dimensional graphics processing, and three-dimensional image processing is performed together with two-dimensional image display operation so that display is made on a display device to be visually recognized with ease by an operator.
2. Description of the Related Art
A radar apparatus has been hitherto installed on a ship. When the ship is navigated, the ship is operated while observing the situation of the target around the navigation route by using the radar apparatus. Thus, the ship is navigated safely. As well-known in the art, such a radar apparatus is operated as follows. That is, a transmission radio wave, which is transmitted from a rotating antenna, is reflected by a target. A reflected radio wave therefrom is received to display a concentric circular image depicted about a center of its own position on a display unit.
In such a system, the intensity of the reflected radio wave is displayed as a difference in brightness of a point at which the target exists, for example, on a screen of the display unit of the raster scan type.
When such a radar apparatus is used, it is possible to observe an objective moving ship which approaches a subjective ship during its navigation and anchorage. Further, it is possible to monitor whether or not the subjective ship is deviated from an anchorage position, for example, due t o a tide, on the basis of the reflected radio wave from a fixed reflecting object.
In general, when such a display unit equipped for the ship radar apparatus is operated, the target point on a screen is displayed in a two-dimensionally designed manner as in a plan view, in which the image is not displayed, for example, on the basis of the height of the target. The height and the size of the target have been judged depending on the brightness per pixel of the target displayed on the screen on the basis of the intensity of the reflected radio wave from the target.
Therefore, an inconvenience arises in that the judgement on the size of the target displayed on the radar screen differs depending on the operator of the radar apparatus. If any numerical expression based on the intensity of the reflected radio wave from the target is adopted for the height and the size of the target in order to avoid the inconvenience as described above, a large amount of data is dealt with as in the case of general image data. As a result, another inconvenience arises in that it is difficult for the radar operator to visually recognize the height and the size of the target with ease at a glance when the radar operator make judgement on the displayed numerical information.
In order to dissolve the problem as described above, the present applicant has suggested a radar apparatus which makes it possible to three-dimensionally display a target on a display unit screen so that, for example, the target is effectively detected, even by a user who is not accustomed to the radar observation so much (see Japanese Patent Publication No. 8-30732).
The three-dimensionally designed display radar disclosed in this patent document comprises a radar transmitting/receiving unit for deriving orientation information, distance information, and reception intensity information from a target respectively; a display device; a three-dimensionally designed coordinate converter for converting the orientation information and the distance information into XY coordinate values based on a perspective projection drawing method, and converting the reception intensity information into a signal for indicating a height of the target with a length of a straight line; a marker-generating means for sending a lattice-shaped or a concentric-shaped distance marker signal when three-dimensional display is made on a screen of the display device; and a storage means provided with a storage address corresponding to each of picture elements on the display device, for storing the reception intensity information in the storage address corresponding to the XY coordinates obtained by the three-dimensionally designed coordinate converter when the three-dimensionally designed display is made, and storing the marker signal so that they are successively read to send an image signal to the display device.
In the disclosed three-dimensionally designed display radar, the orientation information and the distance information obtained by the radar transmitter/receiver are converted into the XY coordinate values based on the perspective projection drawing method, and the reception intensity information is converted into the signal for indicating the height of the target with the length of the straight line so that the display is made on the display device.
Therefore, the three-dimensionally designed display radar disclosed in the patent document described above is not operated such that the target observed by using the radar apparatus is displayed in a real shape, i.e., as a real image as in the three-dimensional graphics (computer graphics).